Given 4 flags of different colours, how many different signals can be generated, if a signal requires the use of 2 flags one below the other?

Explanation

To solve the problem of how many different signals can be generated using 2 flags from a set of 4 flags of different colors, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Total Flags**: We have a total of 4 flags, each of a different color.

2. **Choose the First Flag**: For the first position in the signal (the top flag), we can choose any of the 4 flags. Therefore, there are 4 options for the first flag.

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